The present invention relates to a device for the transdermal delivery of a drug.
The transdermal delivery of a drug is frequently done by a "passive patch" or an "active patch" applied to the skin of the patient. A passive patch employs chemical potential as the driving force to deliver the drug, whereas an active patch employs an electrical potential as the driving force to deliver the drug.
Various types of active patches have been described in the literature based on iontophoresis (or electrophoresis or electroosmosis), wherein ionic (charged) molecules of the drug are delivered to the skin tissue of the patient by the passage of electric current through an electrolyte solution containing the drug. In such a technique, the drug to be delivered is contacted by only one of the electrodes. Thus, contacting the drug by the anode electrode produces positive ions which are driven into the skin at the anode, and contacting the drug with the cathode electrode produces ions with negative charges which are driven into the cathode. A review of this technique appears in the article titled "Iontophoretic Delivery of Drugs: Fundamentals, Developments and Biomedical Applications" by Ajay K. Banga and Yie W. Chien, Journal of Controlled Release, 7 (1988) 1-24.
The main drawback in the iontophoresis delivery of a drug is the danger of electric shock, skin irritation or burns, since the electrodes are in direct contact with the patient's skin. Thus, the rate of delivery of the drug to the skin is generally linearly proportional to the density of the electrical current supplied, but the power required, or heat generated, is generally proportional to the square of the electrical current supplied.